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Abstract Hydrophosphination activity has been solicited from the parent and decamethyl zirconocene dichloride compounds, Cp2ZrCl2and Cp*2ZrCl2. Given recent reports of photocatalytic hydrophosphination, these compounds were irradiated in the near ultraviolet (UV) as precatalysts resulting in the successful hydrophosphination of styrene substrates and activated alkenes. Irradiation appears to induce homolysis of the Cp or Cp* ligand, resulting in radical hydrophosphination. Successful detection of this radical reactivity was achieved by monitoring for EPR signals within situirradiation, a methodology proving to be general for the determination of radical versus closed‐shell reactivity in transition‐metal photocatalysis.
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Photocatalytic Hydrophosphination Using Calcium Precatalysts
Abstract Hydrophosphination using calcium compounds as catalysts under irradiation is described as a foray into s‐block photocatalysis. Transition‐metal compounds have been highly successful hydrophosphination catalysts under photochemical conditions, utilizing substrates previously considered inaccessible. A calcium hydrophosphination precatalyst, Ca(nacnac) (THF) (N(SiMe3)2) (1, nacnac = HC[(C(Me)N‐2,6‐iPr2C6H3)]2), reported by Barrett and Hill, as well as the presumed intermediate, Ca(nacnac) (THF) (PPh2) (2), and the Schlenk equilibrium product, Ca[N(SiMe3)2]2(THF)2(3) were screened under photochemical conditions with a range of unsaturated substrates including styrenic alkenes, Michael acceptors, and dienes with modest to excellent conversions, though unactivated alkenes were inaccessible. All compounds exhibit enhanced catalysis under irradiation by light emitting diode (LED)‐generated blue light. Nacnac‐supported compounds generate radicals as evidenced by Electron Paramagnetic Resonance (EPR) spectroscopy and radical trapping reactions, whereas unsupported calcium compounds are EPR silent and appear to undergo hydrophosphination akin to thermal reactions with these compounds. These results buttress the notion that photoactivation of π‐basic ligands is a broad phenomenon, extending beyond the d‐block, but like d‐block metals, consideration of ancillary ligands is essential to avoid radical reactivity.
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- PAR ID:
- 10586016
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 31
- Issue:
- 36
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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